Selective recovery or separation of organic ions, e.g., organic anions or cations, from solution is a crucial challenge in the chemical and pharmaceutical industries, and in environmental remediation efforts such as in large-scale wastewater treatment facilities. For example, chemical pollutants in ultra-dilute concentrations (e.g., organic endocrine disruptors, pesticides, household chemicals, dyes and heavy metal cations), which are classified by the EPA as contaminants of emerging concern, pose a particularly vexing problem in wastewater treatment, since existing technologies suffer from high energetic penalties and performance limitations when confronted with pollutants at these very low concentrations (nM to μM) with competing species in excess. These compounds often originate from high-level chemical manufacturing, and can have a strong detrimental impact on the aquatic environment and human health.
Traditional separation methods, such as physiochemical adsorption, coagulation, capacitive deionization (CDI), chemical oxidation, and membrane processes (e.g., reverse osmosis, nano-filtration, electro-dialysis), typically suffer from one or more of the following drawbacks: low ion specificity and selectivity, lack of regenerability of adsorbent materials, requirement for high temperature and/or pressure, high operating costs, and generation of secondary pollutants in the process. Grimm et al. (1998) Desalination 115: 285-294; Suss et al. (2012) Energy & Environmental Science 5; 9511-9519; Subramani et al. (2011) Water Research 45: 1907-1920. Accordingly, efficient, affordable and robust purification technologies are needed for a range of separation contexts, from point-of-source treatment or remote in-situ purification devices to large-scale wastewater treatment facilities.